The Collaborative International Dictionary of English v.0.48:

Heedless \Heed"less\, a.
   Without heed or care; inattentive; careless; thoughtless;
   unobservant.
   [1913 Webster]

         O, negligent and heedless discipline!    --Shak.
   [1913 Webster]

         The heedless lover does not know
         Whose eyes they are that wound him so.   --Waller.
   -- Heed"less*ly, adv. -- Heed"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heedlessness
    n 1: a lack of attentiveness (as to children or helpless people)
         [syn: inattentiveness, heedlessness] [ant:
         attentiveness, heed, paying attention, regard]
    2: the trait of acting rashly and without prudence [syn:
       heedlessness, mindlessness, rashness]
    3: the trait of forgetting or ignoring your responsibilities
       [syn: unmindfulness, heedlessness, inadvertence,
       inadvertency] [ant: heedfulness, mindfulness]